refact: 重构代码生成 (#72)

Reviewed-on: PostGuard/Canon#72

Canon.Core/CodeGenerators/CCodeBuilder.cs

@@ -10,16 +10,65 @@ public class CCodeBuilder
 {
     private readonly StringBuilder _builder = new();
 
-    /// <summary>
-    /// 符号表
-    /// </summary>
-    public SymbolTable SymbolTable { get; } = new();
+    private int _scopeCount = 0;
+    private string _scopeEmpty = string.Empty;
 
     public void AddString(string code)
     {
         _builder.Append(code);
     }
 
+    public void AddLine(string code)
+    {
+        foreach (string line in code.Split('\n'))
+        {
+            _builder.Append(_scopeEmpty);
+            _builder.Append(line);
+            _builder.Append('\n');
+        }
+    }
+
+    /// <summary>
+    /// 开始一段代码块
+    /// </summary>
+    public void BeginScope()
+    {
+        _builder.Append(_scopeEmpty).Append("{\n");
+
+        _scopeCount += 1;
+        string scopeEmpty = string.Empty;
+
+        for (int i = 0; i < _scopeCount; i++)
+        {
+            scopeEmpty += "    ";
+        }
+
+        _scopeEmpty = scopeEmpty;
+    }
+
+    /// <summary>
+    /// 结束一段代码块
+    /// </summary>
+    public void EndScope()
+    {
+        if (_scopeCount <= 0)
+        {
+            throw new InvalidOperationException("The scope has been closed!");
+        }
+
+        _scopeCount -= 1;
+
+        string scopeEmpty = string.Empty;
+
+        for (int i = 0; i < _scopeCount; i++)
+        {
+            scopeEmpty += "    ";
+        }
+
+        _scopeEmpty = scopeEmpty;
+
+        _builder.Append(_scopeEmpty).Append("}\n");
+    }
 
     public string Build()
     {